Teleology in biology is the use of the language of goal-directedness in accounts of evolutionary adaptation, which some biologists and philosophers of science find problematic. The term teleonomy has also been proposed. Before Darwin, organisms were seen as existing because God had designed and created them; their features such as eyes were taken by natural theology to have been made to enable them to carry out their functions, such as seeing. Evolutionary biologists often use similar teleological formulations that invoke purpose, but these imply natural selection rather than actual goals, whether conscious or not. Some biologists and religious thinkers held that evolution itself was somehow goal-directed (orthogenesis), and in vitalist versions, driven by a purposeful life force. With evolution working by natural selection acting on inherited variation, the use of teleology in biology has attracted criticism, and attempts have been made to teach students to avoid teleological language.
Nevertheless, biologists still often write about evolution as if organisms had goals, and some philosophers of biology such as Francisco Ayala and biologists such as J. B. S. Haldane consider that teleological language is unavoidable in evolutionary biology.
Context
Teleology
Teleology (Greek τέλος, telos "end, purpose" and -λογία, logia, "a branch of learning") was coined by the philosopher Christian von Wolff in 1728. The concept derives from the ancient Greek philosophy of Aristotle, where the final cause (the purpose) of a thing is its function. However, Aristotle's biology does not envisage evolution by natural selection.
Phrases used by biologists like "a function of ... is to ..." or "is designed for" are teleological at least in language. The presence of real or apparent teleology in explanations of natural selection is a controversial aspect of the philosophy of biology, not least for its echoes of natural theology.
Natural theology
Before Darwin, natural theology both assumed the existence of God and used the appearance of function in nature to argue for the existence of God. The English parson-naturalist John Ray stated that his intention was "to illustrate the glory of God in the knowledge of the works of nature or creation". Natural theology presented forms of the teleological argument or argument from design, namely that organs functioned well for their apparent purpose, so they were well-designed, so they must have been designed by a benevolent creator. For example, the eye had the function of seeing, and contained features like the iris and lens that assisted with seeing; therefore, ran the argument, it had been designed for that purpose.
Immanuel Kant agreed that living things are built with a design, but as nature lacks a designer, it could only mean, as he argued in his book Thoughts on the True Estimation of Living Forces, that living beings are naturally teleological and incapable of being explained purely by a framework of forces like Newton's laws of motion.
Goal-directed evolution
Religious thinkers and biologists have supposed that evolution was driven by some kind of life force, a philosophy known as vitalism, and have often supposed that it had some kind of goal or direction (towards which the life force was striving, if they also believed in that), known as orthogenesis or evolutionary progress. Such goal-directedness implies a long-term teleological force; some supporters of orthogenesis considered it to be a spiritual force, while others held that it was purely biological. For example, the embryologist Karl Ernst von Baer believed in a teleological force in nature,Barbieri, Marcello. (2013). Biosemiotics: Information, Codes and Signs in Living Systems. Nova Science Publishers. p. 7. Jacobsen, Eric Paul. (2005). From Cosmology to Ecology: The Monist World-view in Germany from 1770 to 1930. p. 100. Peter Lang. whereas the spiritualist philosopher Henri Bergson linked orthogenesis with vitalism, arguing for a creative force in evolution known as élan vital in his book Creative Evolution (1907).Bowler, Peter J. (1992). The Eclipse of Darwinism: Anti-Darwinian Evolution Theories in the Decades around 1900. The Johns Hopkins University Press. pp. 116–117. The biophysicist Pierre Lecomte du Noüy and the botanist Edmund Ware Sinnott developed vitalist evolutionary philosophies known as telefinalism and telism respectively. Their views were heavily criticized as non-scientific; the palaeontologist George Gaylord Simpson argued that Du Noüy and Sinnott were promoting religious versions of evolution.Simpson, George Gaylord. (1964). Evolutionary Theology: The New Mysticism. In This View of Life: The World of an Evolutionist. Harcourt, Brace & World. pp. 213–233 The Jesuit paleontologist Pierre Teilhard de Chardin argued that evolution was aiming for a supposed spiritual "Omega Point" in what he called "directed additivity".De Chardin, Pierre Teilhard. (2003, reprint edition). The Human Phenomenon. Sussex Academic Press. p. 65. With the emergence of the modern evolutionary synthesis, in which the genetic mechanisms of evolution were discovered, the hypothesis of orthogenesis was largely abandoned by biologists,Levinton, Jeffrey S. (2001). Genetics, Paleontology, and Macroevolution. Cambridge University Press. pp. 14–16. Montgomery, Georgina M.; Largent, Mark A. (2015). A Companion to the History of American Science. Wiley. p. 218. "With the integration of Mendelian genetics and population genetics into evolutionary theory in the 1930s a new generation of biologists applied mathematical techniques to investigate how changes in the frequency of genes in populations combined with natural selection could produce species change. This demonstrated that Darwinian natural selection was the primary mechanism for evolution and that other models of evolution, such as neo-Lamarckism and orthogenesis, were invalid." especially with Ronald Fisher's argument in his 1930 book The Genetical Theory of Natural Selection.
Natural selection
Natural selection, introduced in 1859 as the central mechanism of evolution by Charles Darwin, is the differential survival and reproduction of individuals due to differences in phenotype. The mechanism directly implies evolution, a change in heritable traits of a population over time.
Adaptation
A trait which persists in a population is often assumed by biologists to have been selected for in the course of evolution, raising the question of how the trait achieves this. Biologists call any such mechanism the function of the trait, using phrases like "A function of stotting by antelopes is to communicate to predators that they have been detected", or "The primate hand is designed (by natural selection) for grasping."
An adaptation is an observable structure or other feature of an organism (for example, an enzyme) generated by natural selection to serve its current function. A biologist might propose the hypothesis that feathers are adaptations for bird flight. That would require three things: that the trait of having feathers is heritable; that the trait does serve the function of flight; and that the trait increases the fitness of the organisms that have it. Feathers clearly meet these three conditions in living birds. However, there is also a historical question, namely, did the trait arise at the same time as bird flight? Unfortunately for the hypothesis, this seems not to be so: theropod dinosaurs had feathers, but many of them did not fly. Feathers can be described as an exaptation, having been co-opted for flight but having evolved earlier for another purpose such as insulation. Biologists may describe both the co-option and the earlier adaptation in teleological language.
Status in evolutionary biology
A problematic issue
Apparent teleology is a recurring issue in evolutionary biology, much to the consternation of some writers, and as an explanatory style it remains controversial. There are various reasons why biologists may find teleology problematic.
Firstly, the concept of adaptation is itself controversial, as it can be taken to imply, as the evolutionary biologists Stephen J. Gould and Richard Lewontin argued, that biologists agree with Voltaire's Doctor Pangloss in his 1759 satire Candide that this is "the best of all possible worlds", in other words that every trait is perfectly suited to its functions. However, all that evolutionary biology requires is the weaker claim that one trait is at least slightly better in a certain context than another, and hence is selected for.
Secondly, teleology is linked to the pre-Darwinian idea of natural theology, that the natural world gives evidence of the conscious design and beneficent intentions of a creator, as in the writings of John Ray. William Derham continued Ray's tradition with books such as his 1713 Physico-Theology and his 1714 Astro-Theology. They in turn influenced William Paley who wrote a detailed teleological argument for God in 1802, Natural Theology, or Evidences of the Existence and Attributes of the Deity collected from the Appearances of Nature, starting with the watchmaker analogy. Such creationism, along with a vitalist life-force and directed orthogenetic evolution, has been rejected by most biologists.
Thirdly, attributing purposes to adaptations risks confusion with popular forms of Lamarckism where animals in particular have been supposed to influence their own evolution through their intentions, though Lamarck himself spoke rather of habits of use, and the belief that his thinking was teleological has been challenged.
Fourthly, the teleological explanation of adaptation is uncomfortable because it seems to require backward causation, in which existing traits are explained by future outcomes; because it seems to attribute the action of a conscious mind when none is assumed to be present in an organism; and because, as a result, adaptation looks impossible to test empirically.
A fifth reason concerns students rather than researchers: Gonzalez Galli argues that since people naturally imagine that evolution has a purpose or direction, then the use of teleological language by scientists may act as an obstacle to students when learning about natural selection. Such language, he argues, should be removed to make teaching more effective.
Removable teleological shorthand
Statements which imply that nature has goals, for example where a species is said to do something "in order to" achieve survival, appear teleological, and therefore invalid to evolutionary biologists. It is however usually possible to rewrite such sentences to avoid the apparent teleology. Some biology courses have incorporated exercises requiring students to rephrase such sentences so that they do not read teleologically. Nevertheless, biologists still frequently write in a way which can be read as implying teleology, even though that is not their intention. John Reiss argues that evolutionary biology can be purged of apparent teleology by rejecting the pre-Darwinian watchmaker analogy for natural selection; other arguments against this analogy have also been promoted by writers such as the evolutionary biologist Richard Dawkins.